1. Technical Field
The present invention relates to a robot and a manufacturing method for a robot. Specifically, the present invention relate to a robot having a multi-joint arm.
2. Related Art
Industrial robots have been used in assembling lines for industrial products or welding process lines in a factory to achieve automation and energy-saving system. In recent years, because work processes are complicated due to smaller size and high functionality of industrial products, a multi-axis control having a multi-joint arm in which an arm member including a plurality of links and joints is rotatably fixed to a driving axis (a rotational axis) is desired. For example, JP publication No. 2010-167515 discloses a robot in which a six-axis multi-joint arm is provided at each side of a base (a body). The six-axis multi-joint arm is configured with a shoulder member, an upper arm member, a forearm member and a wrist member to perform as a human arm. An end effector, such as a robot hand, that performs certain work by a robot is attached to a tip of a link that acts as a wrist member of the multi-joint arm.
Further, a seventh-axis multi-joint arm is developed in the recent years. The seventh-axis multi-joint arm has a twist operation arm (joint) and a bending and stretching operation arm (joint) that are alternatively connected to the upper arm member to perform as a real human arm operation.
As discussed above, when the human work is replaced by industrial robot work for the automation, a size of a robot is required as a size of a human to place them in existing lines of a factory. Thus, further smaller size of a robot is desired. In a robot having the six- or seventh-axis multi-joint arm, a joint configuration that rotatably connects and drives adjacent links is a bottleneck when a movement freedom of an end effector in connection with an arm movement increases and a size is miniaturize. The key is a downsized writ member as a link. The most end of a bending and stretching rotational axis to which an end effector is attached is connected to the link. In other words, a hand to which the end effector is attached is rotatably connected to the link around a twist-rotational axis.
At least a motor that is configured with a rotor that rotates a hand around the twist-rotational axis, a rotor shaft, a stator and housing is assembled in the twist member. JP publication No. S62-241689 discloses a robot in which a member that forms an outer cover of an arm member (a wrist member) is used as housing to make a compact wrist member.
However, because the housing that holds and positions a motor is the outer cover of the wrist member in JP publication No. S62-241689, heat that is generated by the motor operation is directly transferred to the wrist member. As a result, there is a possibility that mechanical problems caused by the heat may occur. Further, when a driving element, such as an encoder, assembled to the wrist member is located in the housing, the heat may cause a position detection error of the encoder so as to affect robot operations.
A robot arm configured by coupling a plurality of arm sections and a robot including the robot arm have been known (see, for example, Patent Literature 1). In the robot arm, a coupling portion of the arm sections is a joint. The arm sections can be bent or twisted by the joint. The external shape of each of the arm sections is formed in a pillar shape (e.g., a columnar shape). The outer diameter of the arm section is substantially fixed along the center axis direction thereof.
The related art is described in JP-A-2010-284777.
However, when the arm sections having the substantially fixed outer diameter are bent by the joint between the arm sections, since the outer diameter is fixed, the outer circumferential section of one arm section and the outer circumferential section of the other arm section interfere with each other (collide with each other) relatively early after the start of the bending. Therefore, a movable range (a turning range) of the arms is relatively narrow.